1. Field of the Invention
This invention relates in general to the art of coating and in particular to wick-type coating apparatus for use with liquid coating compositions. More specifically, this invention relates to a novel coating apparatus which functions by the principle of wicking and is especially advantageous for use in the coating of discrete sheets of material but can also be used in the coating of continuous webs.
2. Description of the Prior Art
In wick-type coating apparatus, the wick can be used to transfer the coating composition to the peripheral surface of a roller which, in turn, applies the coating composition to the surface of the article to be coated. See, for example, U.S. Pat. Nos. 1,454,362, 1,454,364, and 3,831,553, British Pat. No. 1,388,483, and Item No. 13622, Research Disclosure, August, 1975. Alternatively, the wick can be arranged to come into direct contact with the surface to be coated. See, for example, U.S. Pat. Nos. 1,454,364, 2,348,067, 2,646,770, 3,000,349 and 3,786,736, and British Pat. No. 1,388,483. Wick-type coating apparatus can be used to apply coating compositions to discrete sheets or to continuous webs. Difficulties are often encountered, however, in achieving uniform coating. This is the case both with devices of the type where the wick transfers the coating composition to a roller and of the type where it applies it directly and is especially true in regard to coating a succession of discrete sheets where it is often extremely difficult to obtain highly uniform coatings which are free from skips and streaks. Problems of spillover at the lead and/or trailing edges of a discrete sheet, and resulting unwanted deposition of coating composition on the edges of the sheet, are also commonly encountered.
It is toward the objective of providing a wick-type coating apparatus which is capable of coating both continuous webs and discrete sheets, and of applying liquid coating composition thereto in a highly uniform manner, that the present invention is directed.